Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily—and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming.

/pdf/persistence-of-soil-organic-matter-as-an-ecosystem-property-ago0khy192.pdf

Persistence of soil organic matter as an ecosystem property

Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

/pdf/climate-change-2007-the-physical-science-basis-1x93ttz9jt.pdf

Climate Change 2007: The Physical Science Basis.

Soil amendment with biochar is evaluated globally as a means to improve soil fertility and to mitigate climate change. However, the effects of biochar on soil biota have received much less attention than its effects on soil chemical properties. A review of the literature reveals a significant number of early studies on biochar-type materials as soil amendments either for managing pathogens, as inoculant carriers or for manipulative experiments to sorb signaling compounds or toxins. However, no studies exist in the soil biologyliterature that recognize the observed largevariations ofbiochar physico-chemical properties. This shortcoming has hampered insight into mechanisms by which biochar influences soil microorganisms, fauna and plant roots. Additional factors limiting meaningful interpretation of many datasets are the clearly demonstrated sorption properties that interfere with standard extraction procedures for soil microbial biomass or enzyme assays, and the confounding effects of varying amounts of minerals. In most studies, microbial biomass has been found to increase as a result of biochar additions, with significant changes in microbial community composition and enzyme activities that may explain biogeochemical effects of biochar on element cycles, plant pathogens, and crop growth. Yet, very little is known about the mechanisms through which biochar affects microbial abundance and community composition. The effects of biochar on soil fauna are even less understood than its effects on microorganisms, apart from several notable studies on earthworms. It is clear, however, that sorption phenomena, pH and physical properties of biochars such as pore structure, surface area and mineral matter play important roles in determining how different biochars affect soil biota. Observations on microbial dynamics lead to the conclusion of a possible improved resource use due to co-location of various resources in and around biochars. Sorption and therebyinactivation of growth-inhibiting substances likelyplaysa rolefor increased abundance of soil biota. No evidence exists so far for direct negative effects of biochars on plant roots. Occasionally observed decreases in abundance of mycorrhizal fungi are likely caused by concomitant increases in nutrient availability,reducing theneedfor symbionts.Inthe shortterm,therelease ofavarietyoforganic molecules from fresh biochar may in some cases be responsible for increases or decreases in abundance and activity of soil biota. A road map for future biochar research must include a systematic appreciation of different biochar-types and basic manipulative experiments that unambiguously identify the interactions between biochar and soil biota.

http://www.css.cornell.edu/faculty/lehmann/pictures/publ/SoilBiolBiochem%2043,%201812–1836,%202011%20Lehmann.pdf

Biochar effects on soil biota – A review

Biochar as a sorbent for contaminant management in soil and water: a review.

Production of biochar (the carbon (C)-rich solid formed by pyrolysis of biomass) and its storage in soils have been suggested as a means of abating climate change by sequestering carbon, while simultaneously providing energy and increasing crop yields. Substantial uncertainties exist, however, regarding the impact, capacity and sustainability of biochar at the global level. In this paper we estimate the maximum sustainable technical potential of biochar to mitigate climate change. Annual net emissions of carbon dioxide (CO 2 ), methane and nitrous oxide could be reduced by a maximum of 1.8 Pg CO 2 -C equivalent (CO 2 -C e ) per year (12 % of current anthropogenic CO 2 -C e emissions; 1 Pg = 1 Gt), and total net emissions over the course of a century by 130 Pg CO 2 -C e , without endangering food security, habitat or soil conservation. Biochar has a larger climate-change mitigation potential than combustion of the same sustainably procured biomass for bioenergy, except when fertile soils are amended while coal is the fuel being offset.

/pdf/sustainable-biochar-to-mitigate-global-climate-change-54jjaa8usw.pdf

Sustainable biochar to mitigate global climate change

http://www.css.cornell.edu/faculty/lehmann/publ/OrgGeochem%2037,%201477-1488,%202006%20Cheng%20www.pdf

Oxidation of Black Carbon by Biotic and Abiotic Processes

http://www.css.cornell.edu/faculty/lehmann/publ/GeochimCosmochimActa%2072,%201598-1610,%202008%20Cheng.pdf

Natural oxidation of black carbon in soils: Changes in molecular form and surface charge along a climosequence

[1] The recalcitrant properties of black carbon (BC) grant it to be a significant pool of stable organic C (OC) in soils. Up to now, however, the longevity of BC under different climates is still unclear. In this study, we used BC samples from historical charcoal blast furnace sites to examine the stability of BC across a climatic gradient of mean annual temperatures (MAT) from 3.9 to 17.2°C. The results showed that OC concentration and OC storage in the BC-containing soils at a soil depth of 0–0.2 m were 9.0 and 4.7 times higher than those in adjacent soils, respectively. Organic C in the BC-containing soils was more stable, with a significantly lower amount of the labile OC fraction (4.4 mg g−1 OC versus 27.5 mg g−1 OC) and longer half-life of the recalcitrant OC fraction (59 years versus 9 years) than the adjacent soils determined by incubation experiments. The stability of BC was primarily due to its inherently recalcitrant chemical composition as suggested by short-term incubation and solid state 13C nuclear magnetic resonance spectra of isolated BC particles. A significant negative relationship between OC storage and MAT further indicated that OC storage was decreased with warmer climate. However, the lack of a relationship between MAT and BC mineralization suggested that the stability of the remaining BC was similar between sites with very different MAT. Despite the fact that warming or cooling result in immediate consequences for BC stocks, it may have little impact on the stability of remaining BC over the period studied.

http://www.css.cornell.edu/faculty/lehmann/publ/JGeophysRes%20113,%20G02027,%202008%20Cheng.pdf

Stability of black carbon in soils across a climatic gradient

http://www.css.cornell.edu/faculty/lehmann/publ/Chemosphere%2075,%201021-1027,%202009%20Cheng.pdf

Chih-Hsin Cheng

Papers

Oxidation of Black Carbon by Biotic and Abiotic Processes

Natural oxidation of black carbon in soils: Changes in molecular form and surface charge along a climosequence

Stability of black carbon in soils across a climatic gradient

Ageing of black carbon along a temperature gradient.

Biodegradation of phthalate esters by two bacteria strains.